Hydraulic actuators are utilized in various industrial and other applications to provide movement in opposite directions under the control of hydraulic fluid supplied by a control valve unit. For example, material handling systems, conveyors, various metal removal machines, cold and hot forming machines, indexers, automatic loaders, and door positioners, etc. utilize hydraulic actuators to control positioning of components during operation.
Most hydraulic actuators are of the linear type and thus provide linear movement and positioning; however, some hydraulic actuators are of the rotary type and provide rotary motion and positioning. Hydraulic linear actuators are most often embodied by cylinders which include a housing and a piston that is received within the housing and has a connecting rod extending outwardly therefrom in order to provide connection of the cylinder for actuating movement. A bore within the cylinder housing receives the piston in a sealingly slidable relationship such that hydraulic fluid supplied to one or the other sides of the piston provides piston movement and accompanying driving of the associated connecting rod. Some hydraulic cylinders have two connecting rods extending from the piston thereof so as to have equal amounts of fluid supplied to the cylinder on one side of the piston thereof and ejected from the cylinder on the other side of the piston. However, the more conventional cylinder has only a single connecting rod and thus has a different area on the side thereof having the connecting rod than the area of the side thereof without any connecting rod. As such, different amounts of fluid are supplied to and ejected from such a cylinder during hydraulically actuated movement of its piston. One of the most common constructions of hydraulic cylinders incorporates a tubular housing and square end caps that are held in position against ends of the housing by through-bolts extending alongside the housing and through the corners of the end caps.
The U.S. patent of Barlow U.S. Pat. No. 3,954,045 is assigned to the assignee of the present invention and discloses a control unit for a hydraulic rotary actuator. This control unit includes a valve that supplies hydraulic fluid to the rotary actuator under the control of a solenoid assembly and a cam mechanism in order to control actuator rotation. The solenoid assembly opens the supply valve to initiate the hydraulically actuated rotation. Cams of the cam mechanism are contoured to close the supply valve and thereby terminate the actuator movement with a feedback action.
U.S. patent application Ser. No. 014,175, filed Feb. 22, 1979, is assigned to the assignee of the present invention and discloses a control valve unit for a hydraulic actuator of either the linear or the rotary type. This control valve unit includes a supply valve that is opened at a predetermined rate to control acceleration and closed by cams to provide deceleration of the actuator movement by a feedback action.
Other hydraulic control valves are disclosed by U.S. Pat. Nos. Re. 29,392; 2,879,644; 3,640,069; 3,693,385; 3,779,136; and 3,780,623.